Spiral cut teeth to provide a positive grip to remove rounded or damaged bolts. Can also be used on screw heads and studs. Will fit heads sized 9, 10, 11, 12, 13, 14, 15, 16, 17 and 19mm. 1 X 7MM X 90MM bar Can be driven with a 3/8" drive ratchet or metric spanner. Manufactured from Chrome Molybdenum steel for strength and durability. This Set allows you to extract hex bolts which are Damaged or seized For removal without damaging the casing or thread. Reverse left handed threaded sockets. For use with a 3/8" drive ratchet, socket or spanner.